Observation of Intricate Chiral Optical Force in a Spin-Curl Light Field.

Harnessing chiral optical forces facilitates numerous applications in enantioselective sorting and sensing. To date, significant challenges persist in substantiating the holistic complex theorem of these forces as experimental demonstrations employ common light waves (e.g., Gaussian beams and evanescent waves), showcasing the reversal of optical force against handedness (light's or particle's). Here, we elucidate the cooperative significance of incorporating multiple optical forces to generate an intricate chiral optical force in a complex spin-curl field. The interplay of distinct light properties (the transverse spin, Belinfante spin momentum, and energy vortex) is found to induce abnormal phenomena. For instance, this intriguing total force not only reverses its sign with particle handedness but also correlates strongly with particle size and light helicity. Experimental measurements of quasi-achiral and chirality-determined forces manifest our research as a paradigm for testing the holistic optical-force theorem on chiral particles, which is unattainable by previous reports that only affirm a specific type of chiral optical forces. Our study offers wide applications in chiral sensing, sorting, spintronics, metamaterials, etc.